1. Field of the Invention
The present invention relates to a logic analyzer for measuring logic signals, more particularly for measuring data signals delivered by a number of targets which are uncorrelated in time.
2. Description of the Prior Art
Digital electronic devices comprise microprocessors which co-operate and implement complex functions. Appropriate measuring instruments are needed to develop, calibrate and test such devices.
The accompanying FIG. 1 shows the construction of a conventional logic analyzer 14. Such conventional analyzers have a clock selector 15 which selects, and delivers at its output either an external clock signal derived from a target 11 and supplied to the analyzer by way of a line 12, or an internal clock signal delivered by a clock signal generator 16. The analyzer also contains a data memory 17 for the purpose of storing data signals which are delivered from the target 11 by way of data lines 13.
The data signals are sampled by means of the clock signal at the clock selector output. Storage of data signals in the memory 17 is stopped by a trigger control 18 when a predetermined trigger condition has been fulfilled. An evaluator 19 contains a data processor and an input/output unit, and operates to evaluate the stored data signals, to input instructions and to display the required representation of the stored data signals.
These known logic analyzers can measure only data signals of discrete targets, for example discrete microprocessors, with the trigger control being unable to take into account time relationships between the data signals of different targets.
A known logic analyzer (EP-AO 181 619) embodies both a first analyzer section and a second analyzer section The first analyzer section can be used, for example, to make a state analysis of a first block of data signals. The second analyzer section is used, for example, to make a time analysis of a second block of data signals. The first analyzer section has both a time measurement circuit which detects the time intervals of all the samplings in the first analyzer section, and a time interval memory in which the measured intervals are stored. This analyzer also has a time difference measurement circuit for measuring, and a time difference memory for storing, the time interval between the end of recording in the first analyzer section and the end of recording in the second analyzer section.
On the basis of the values stored in the time interval memory and time difference memory the post-triggering processing of the recorded data signals makes it possible to produce a time-correlated representation of the data signals recorded by the first and second analyzer sections. However, this is possible only for two analyzer sections--i.e., only for two different blocks of data signals. In this known logic analyzer the time relationship between the measured data signals cannot also be taken into account for the trigger control.
The testing or examination of complex digital systems, usually involves a number of co-operating micro-processors. It is desirable to use the actual duration of time-uncorrelated data or word zones in data signals derived from a number of different microprocessors--i.e., different targets, and/or the actual time interval between such data or word zones as a criterion for trigger and recording control.
It is an object of the present invention to provide a logic analyzer which uses the actual timing of time uncorrelated data as such control criterion.